Absorption spectrum in chlorophyll

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SUMMARY

The discussion centers on the broad peaks observed in the absorption spectrum of chlorophyll, which contradict the expectation of sharp peaks based on the principle that photon wavelengths must match the energy differences between atomic states. The complexity of chlorophyll, a molecule composed of numerous atoms, contributes to this broadening. Additionally, the conversation highlights the significant number of photons required for photosynthesis, specifically noting that approximately 24 photons are needed to produce one monosaccharide molecule through the Calvin cycle.

PREREQUISITES
  • Understanding of quantum mechanics principles related to photon absorption
  • Basic knowledge of chlorophyll structure and function
  • Familiarity with the Calvin cycle in photosynthesis
  • Knowledge of energy units, specifically electronvolts (eV)
NEXT STEPS
  • Research the molecular structure of chlorophyll and its impact on absorption spectra
  • Study the principles of broadening in absorption spectra, including Doppler and pressure broadening
  • Explore the Calvin cycle in detail, focusing on the role of RuBisCO and photon requirements
  • Investigate the energy conversion processes in photosynthesis and their efficiency
USEFUL FOR

Students and researchers in biochemistry, molecular biology, and plant physiology, as well as educators seeking to explain the complexities of photosynthesis and chlorophyll's role in light absorption.

annnna
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I have a question.

We claim that the wavelength of a photon must exactly match the difference between the states of an atom or molecule. Then why are the peaks in the absorption spectrum of chlorophyll so broad? Shouldn’t they be very sharp?
 
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annnna said:
I have a question.

We claim that the wavelength of a photon must exactly match the difference between the states of an atom or molecule. Then why are the peaks in the absorption spectrum of chlorophyll so broad? Shouldn’t they be very sharp?
No, because it's a complex molecule, made of many tens of atoms:
http://en.wikipedia.org/wiki/Chlorophyll
 
lightarrow said:
No, because it's a complex molecule, made of many tens of atoms:
http://en.wikipedia.org/wiki/Chlorophyll
How come it takes so many photons to make a single sugar molecule via the C3 (Calvin) cycle photosynthesis? The heat of oxidation (to 6CO2 and 6H2O) of C6H12O6 is about 29 eV per molecule. Peaks in the absorption spectrum are less than ~2 eV per photon, so this implies over 15 photons per molecule. In fact studying the RuBisCO cycle implies ~4 photons per CH2O group, or ~24 photons per simple sugar molecule (monosaccharide). How many said photons have to hit the RuBisCO molecule in a millisecond to make the sugar molecule?

Bob S
 
Last edited:

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